The present invention relates to an improvement in an indexing rotary blow molding macine for making a product such as a bottle, container, or other hollow object from thermoplastic resin material. An aspect of the invention relates to such a machine for blow molding such a product form polyethylene terephthalate (PET). An aspect of the invention is a machine to blow mold a plurality of PET bottles from preforms which in turn have been injection molded at one of the work stations on the machine.
Without intending to be limited thereto, the present invention will be described with reference to an indexing rotary injection stretch blow molding machine for making bottles from PET. The general type and construction of such a machine is already known and is described in a number of patents and publications. The state of the art embraces a four station indexing rotary machine for: at a first station injection molding preforms each shaped like a test tube; at a second station heating and/or cooling or both to adjust the temperature level and heat content of the preforms to a level suitable for blow molding; at a third station blow molding the preforms into a bottle; and at the fourth station ejecting the preforms. A neck ring forms part of the injection mold and also serves to hold and move the workpiece molded therein thence and through the cycle of events. The machine then repeats the cycle. Actually, enough mechanism is provided on the machine so that each of the four work stations has work in process at the same time. Moreover, more than one container can be made on the machine at the same time.
A variety of plastics (acrylonitrile, PET) may be used, but a material preferred for making containers, especially those for carbonated beverage bottles, is PET which can be treated on the machine so that the end product bottle is biaxially oriented thereby maximizing the properties of the material while minimizing the quantity of material required.
The present invention is concerned with improving the construction and operation of the blow molding station, e.g. the third station as described above.
As will be seen in the annexed drawings, one state-of-the-art design has the orientation of the neck rings chordal instead of radial. The present machine is described as making at least four bottles at a time where molds and cooperating apparatus are arranged along a chord. Commercial embodiments of the present invention already make six and eight bottles at a time from PET.
In any event, at the blow molding station where the blow molds and neck rings are arranged chordally, there has appeared a significant alignment problem where the blow pin, blow mold, and neck rings have been difficult to get aligned and to keep aligned. Failure to achieve proper alignment results in bottles having necks offset from their bodies and in some instances, flashing. This is because structure of the machine uses a channel shaped frame and the forces clamping the blow mold flex the flanges of the channel and allow misalignment to occur.
The present invention provides an improvement, namely a system for obtaining and keeping alignment among a blowing pin, a neck ring, and the blow mold. This improvement, stated in the simplest and broadest terms is a provision of a toggle system with an overstroke that pushes one of the blow mold halves past center at which point the toggle links assume the well-known straight line and rigidified relationship; the other blow mold half is then driven by hydraulics or pneumatic cylinders into engagement therewith, using such force as is necessary to push the first mentioned mold half back on center. Appropriate means on each mold half engage the neck ring in which the preform has been held all this time.
More specifically, my invention includes in an indexing rotary machine for blow molding more than one bottle at a time from a succession of respective preforms of thermoplastic material by moving said preforms while supported only by the neck from a chordally aligned split neck ring into a position between an initially spaced-apart pair of movable blow molds with each preform being aligned with a female cavity in each blow mold, said split neck ring having at least two parts that are movable relative to each other along a radius extending from the axis about which said ring is rotated in an indexing fashion, the improvement of a system for obtaining and keeping alignment between or among said neck ring and said blow molds which comprises:
a toggle system means for reciprocating one of said blow molds radially relative to said axis between an open position that permits said neck rings with preforms and with bottles blown from such preforms to index in to and away from, respectively, said position between without interference with said one blow mold and at least into the intended alignment at a center position;
a drive means to move the other of said blow molds radially of the machine and into engagement with said one blow mold;
at least one of said toggle system means and drive means for driving that blow mold linked thereto past a predetermined center (intended center) position to an overcenter position and the other of said toggle system means and drive means for driving the remaining said blow mold (remaining mold) against the linked blow mold and both blow molds together from said overcenter position until both molds and neck ring parts are aligned for blowing at the intended center position;
mold contact means on at least one of the aforesaid blow molds, toggle system, and drive means and that one of said neck ring parts closest thereto for establishing contact therebetween after which contact they travel to said overcenter position together; and
bias means on at least one of said blow molds for biasing said neck ring parts together and the neck ring against the other of said blow molds.